Carbon foams are materials of very high carbon content that have appreciable void volume. In appearance, excepting color, carbon foams resemble readily available commercial plastic foams. As with plastic foams, the void volume of carbon foams is located within numerous empty cells. The boundaries of these carbon foam cells are defined by the carbon structure. These cells typically approximate ovoids of regular, but not necessarily uniform, size, shape, distribution, and orientation. The void volumes in these cells typically connects to neighboring void volumes. Such an arrangement is referred to as an open-cell foam. The carbon in these foams forms a structure that is continuous in three dimensions across the material. Typically, the cells in carbon foams are of a size that is readily visible to the unaided human eye. Also, the void volume of carbon foams is such that it typically occupies much greater than one-half of the carbon foam volume.
The regular size, shape, distribution, and orientation of the cells within carbon foam readily distinguishes this material from other materials such as metallurgical cokes. The void volumes within cokes are typically of ovoid shape and of random size, distribution, and orientation. That is, in cokes, some readily visible void volumes can be an order of magnitude, or more, larger than others. It is also not uncommon that the over-lapping of void volumes in cokes results in significant distortions in the void volume shape. These distortions and large void volumes can even lead to a product that has limited structural integrity in all except smaller product volumes. That is, it is not uncommon for coke to be friable and larger pieces of coke to readily break into smaller pieces with very minimal handling. Such breakage is not exhibited by carbon foams. Also, a given sample of coke can exhibit both open and closed-cell void volumes.
Carbon foams have potential utility in a variety of applications as a result of their unique properties such as temperature resistance, strength, and low density. For example, carbon foams can exhibit significant strength, even at extreme temperatures, which makes these materials suitable for use as lightweight thermal barriers, wall panels, and as baffles for high intensity flames. These materials can also function as filter media for the removal of gross solid contaminates from molten metals.
Numerous examples of carbon foams have been produced from various pitches, foamed synthetic plastics, coals, and coal extracts. The resulting carbon foams from each type of feed-stock material exhibit individual properties that make the use of such foams particularly advantageous or disadvantageous in certain applications. For example, pitches (whether they are derived from petroleum or coal) have been shown to produce carbon foams with excellent thermal conductivity but poor mechanical integrity. Coal based foams have excellent mechanical strength, but can sometimes lack the highly ordered crystal structure which is usually associated with high thermal conductivity. Pitch based carbon foams are highly pure due to the extensive processing of the starting raw material that is required. This extensive processing also leads to very high raw material costs, which in turn limits the potential market for the end product.
It would be advantageous to produce a carbon foam that exhibits relatively low density coupled with high strength. It would be further advantageous if such a foam exhibited at least partially the highly ordered crystal structure which is usually associated with high thermal conductivity.